A novel method to determine the concentration of VOCs at atmospheric pressure

Abstract

A novel method to detect the concentration of electronegative VOCs based on the electron attachment rate at atmospheric pressure, through negative discharge in an ion drift tube, is introduced. When the carrier and drift gas in the drift tube are all high-purity nitrogen, electrons are formed by a negative discharge in the ion source, and are injected into the drift region through the shutter grid. When the electronegative sample molecules are continuously introduced into the drift tube from one end, the neutral molecules are ionized through a collision and capture process with the counterflowing swarm of electrons in the drift region. The electron swarm is exponentially diluted as it travels in the drift region. As a result, negative ions are formed in the drift region and a tail appears in the ion mobility spectrum. These spectra include information such as the intensity of the ions and electrons, the drift time, analyte concentration, the electron capture rate etc. The sample concentration can be calculated using the relative equation including information from the spectrum. As examples, in this work the concentration of electronegative samples of CCl₄, CHCl₃, and 1,1,1-C₂H₃Cl₃ are studied when the electron energy is about 0.54 eV. The sample concentrations obtained in the experiment using this method are in good agreement with the initial concentrations created using a syringe pump. The comparison shows that the process of utilizing electron capture information to determine concentration is effective. This study provides a novel method to determine the concentrations of VOCs at atmospheric pressure.